At that point it becomes very not worth taking, which kind of defeats the purpose of the spells. I can see where you're coming from, certainly, but a first level spell that only does one damage? Also, spells do not always drop a die size in damage when they go up or down in level (see: Fireball, Delayed Blast Fireball).
I'm glad you like it, that one was one of the ones I was worried about balance-wise. I basically made a Prismatic version of Flame Blade for it.